An arm of the Pentagon has come under fire for procuring large quantities of apparel from a Nicaraguan factory that labor rights groups say is a sweatshop and that the United States trade representative has voiced serious concerns about.

Several members of Congress say it is wrong for the Pentagon agency, which runs 1,400 stores at military bases and made $7.3 billion in sales last year, to obtain apparel from the Chentex factory, which a Nicaraguan union has accused of firing more than 150 union supporters.

In an unusually stern letter, The United States trade representative, Charlene Barshefsky, warned the Nicaraguan government in October that the United States might rescind some trade benefits unless it moved to ensure that Chentex complied with labor laws.

Labor rights groups in the United States have mounted an intense campaign against Chentex, a factory with 1,800 workers that is owned by the Nien Hsing Textile Company, after Nicaraguan workers accused the company of illegal firings. Many workers also complain about low pay, monitored bathroom visits, large amounts of mandatory overtime and being screamed at and occasionally hit by managers.

Cynthia A. McKinney, Democrat of Georgia, who sits on the procurement subcommittee of the House Armed Services Committee, said it was wrong for one federal agency, the Pentagon, to buy large amounts of apparel from Chentex while another, the trade representative's office, had singled out the factory for criticism.

Representative McKinney and several other House members are working closely with a labor rights group that has obtained shipping documents showing that the Army and Air Force Exchange Service, a nonprofit Pentagon arm that runs the post exchanges, is one of the Chentex's largest customers. Other major customers have included the retailers Wal-Mart and Kohl's.

"The United States government is the last place that should be supporting and coddling sweatshop labor and the violation of human rights," Ms. McKinney said.

Labor rights groups and several House members say the Chentex battle is important because it seeks to upgrade wages and working conditions in poor nations at a time when the American economy is importing more goods than ever and American companies are relocating operations to low-wage countries.

Fred Bluhm, a spokesman for the Army and Air Force Exchange Service, said that in light of the many criticisms of Chentex the exchange service sent officials to Nicaragua to examine the Chentex operation. "Our representative who went there found no problems," he said.

Carlos Yin, the general manager of Chentex, said in a telephone interview that his company treats its workers well. He accused the union of exagerating problems and he insisted that only 12 union supporters had been fired, all of them union leaders. He said they were dismissed legally, asserting that it was the union leaders who had broken the law by calling a one-hour work stoppage and two-day strike without the workers' approval.

"We didn't do anything wrong," Mr. Yin said. "Nicaraguan law protects the workers very strong, and we can't go against the law."

But Charles Kernaghan, executive director of the National Labor Committee, a New York-based labor rights group, said the company dismissed far more than 100 union supporters after they went on strike demanding a 40 percent wage increase.

At a factory that sews 35,000 pair of jeans a day, employees earn about 20 cents for the work they put into a pair of jeans that often sell retail for $30 in the United States. The workers, in effect, demanded to be paid 8 cents more per pair.

Mr. Yin, the factory manager, said all of his workers earn at least the minimum wage, which union leaders say is set unrealistically low in developing countries in order to attract foreign investment.

Last summer, Representative Sherrod Brown, Democrat of Ohio, visited Nicaragua and met mother who worked at Chentex 60 hours a week, while her husband worked at another Nien Hsing factory for 70 hours a week, and yet they lived in a hut with a dirt floor. "The couple had a 3-year-old daughter with discolored tips of her hair, probably from a protein deficiency," he said. "These are people who work 60, 70 hours a week, and their standard of living is just abysmal."

Mr. Brown, who got 67 House members to sign a letter to President Clinton last July about conditions at Chentex and another Nicaraguan factory, Mil Colores, said he would hold a news conference this week criticizing the Army and Air Force Exchange Service.

"I'm outraged that American taxpayers are being made part of this sweatshop global economy in this way," he said.